feat: auto-log deal lifecycle events to activity timeline

[Rishavraaj]

Summary

Enhances the deal activity timeline by automatically logging system events
whenever deal state changes — previously only manual comments were tracked.

Backend

• Inject ActivityService into DealsService and wire it up in the backend
  module factory (sales.module.ts)
• Add optional actorId parameter to all mutating deal service methods so
  events are attributed to the acting user
• Log the following events automatically:

  • deal_created — on deal creation

  • stage_change — when the deal stage changes (stores from/to values)

  • field_update — when title, value, probability, expected close date, or
    priority changes (stores field name, old and new value)

  • deal_closed — when actualCloseDate is set for the first time (stores
    outcome: won/lost and optional lost reason)

  • company_linked / company_unlinked — when a company is added or removed

  • contact_linked / contact_unlinked — when a contact is added or removed

    (with optional role)

  • owner_assigned / owner_removed — when an owner is added or removed

• Update addOwner and removeOwner in DealsRepository to include user
  data so the owner's name is available for activity metadata
• Pass authenticated user ID as actorId from the controller via @Req()

Frontend

• Add renderSystemEventText() helper in ActivityTimeline that maps each
  event type to a human-readable description
• Format field names (camelCase → readable label) and date values (ISO →
  "Mar 27, 2026") for display
• When a field had no previous value, show "set X to Y" instead of
  "updated X from null to Y"
• Render system events in italic muted text, distinct from comment content

No database schema changes — the existing Activity model's activityType
and metadata fields support all new event types.

Screenshot

Test plan

• Create a deal → timeline shows "created this deal"
• Change stage → timeline shows "moved deal from Prospecting to Closed
  Won"
• Set expected close date for first time → shows "set expected close date
  to Mar 27, 2026"
• Update an existing date → shows "updated expected close date from X to
  Y"
• Set actualCloseDate with closed_won stage → shows "marked deal as
  Won"
• Set actualCloseDate with closed_lost + lost reason → shows "marked
  deal as Lost: "
• Link a company → shows "linked company Acme Corp"
• Remove a company → shows "unlinked company Acme Corp"
• Link a contact with a role → shows "linked contact John Doe as Decision
  Maker"
• Remove a contact → shows "unlinked contact John Doe"
• Add an owner → shows "assigned Jane Smith as owner"
• Remove an owner → shows "removed Jane Smith as owner"
• Existing comment create/edit/delete still works unchanged